DESCRIPTION: (Applicant's Abstract) The studies proposed here will investigate the psychopharmacology of cannabinoids in humans. The laboratory-based studies will examine the pharmacological and psychological basis of a broad range of effects of marijuana and 9-tetrahydrocannabinol (THC), including effects relevant both to abuse and to potential therapeutic use. We will measure subjective, or mood-altering, effects (including "euphoria" and "high"), psychomotor and cognitive effects, physiological effects (e.g., heart rate) and drug effects on hunger and food intake. Four studies will investigate the pharmacological and psychological basis of marijuana's effects. First, we will compare the effects of 9-THC to the effects of whole marijuana plant material, using both the oral and the smoked form. Next, we will investigate the effect of varying the rate of onset of 9-THC's effects, by administering the drug intravenously over different infusion durations (i.e., 5 - 20 minutes). In another study, we will investigate the neurochemical basis of the psychoactive effects of 9-THC, by measuring its behavioral and subjective effects after pretreatment with either an opioid antagonist, naltrexone, and a dopamine antagonist, pimozide. The final study will extend previous research conducted in this laboratory on the behavioral interactions between marijuana and alcohol, by investigating whether marijuana or 9-THC ingestion affects consumption of alcohol. We will also investigate whether the effect of cannabinoids on alcohol consumption are related to pharmacology or to expectancy effects. Together, these studies will further our understanding of the pharmacological and environmental determinants of marijuana use, and the effects of 9-THC in humans.